The thermoforming-stamping process for forming reinforced thermoplastic sheets is a process that lies between the forming process of the sheet metal industry and the thermoforming process of plastic industry. On one hand, it is necessary to shape rigid fibers in a composite laminate by pressing them between two mold halves, similarly to the Resin Transfer Molding process or the sheet metal forming process. On the other hand, the heated thermoplastic matrix of the reinforced thermoplastic sheet can better be formed with a vacuum system that allows filling of sharp corners of the part, similar to the thermoforming process of plastic sheets.
The equipment needed for shaping parts made of reinforced thermoplastic sheets includes a thermoforming-stamping press specifically designed for such parts, a sheet supporting equipment allowing tensioning of the sheet, heated ovens, square supporting moving frame to transport the heated sheet from the oven to the forming tools, and a computer based controller to coordinate the molding sequences during all phases of the molding cycle. Two major processes have been used until now to mold parts for medium to high volume productions. The first is the matched-die process that involves the use of two machined steel mold halves, similar to the sheet metal forming industry. The second is the rubber forming process where a rubber male die is used in combination with a machined steel cavity. This process improves the part quality by ensuring good conformation of the reinforced thermoplastic sheet along edges having a small corner radius. It also allows efficient conformation of the part but is rather expensive and difficult to use because the rubber properties must be known precisely and abrasion limits the useful life of the mold. The matched-die forming process for parts made of reinforced thermoplastic sheets is economic for high volume manufacturing of simple parts, but becomes expensive for complex parts because it necessitates the use of a variable thickness mold cavity to ensure complete conformation of the part.
A need therefore exists for an improved molding process and tool for manufacturing parts made of reinforced thermoplastic sheets that overcomes the limits of both the matched die and the rubber forming processes and provides some advantages over them.